RAIKO is a 2U CubeSat designed and developed by students and faculty of Wakayama University, of Wakayama, Japan. The objective is to conduct technology demonstrations on the ISS (International Space Station) that can be utilized for future microsatellites (~ 50 kg), including photographing Earth's surface with a fisheye camera.

RAIKO was developed as part of the UNIFORM (University International Formation Mission) program led by Wakayama University. UNIFORM is funded by a grant from the Nanosatellite Research and Development Project of MEXT (Japanese Ministry of Education, Culture Sports Science and Technology). - As a precursor of the UNIFORM program, RAIKO has been jointly designed, developed, and tested by a team with members from Wakayama University, Tohoku University and the University of Tokyo. 1)2)

Spacecraft:

The nanosatellite is a standard 2U CubeSat with a size of 10 cm x 10 cm x 23 cm and a mass of 2.66 kg. RAIKO features two solar paddles which are deployed after CubeSat release on orbit.

Figure 1: Illustration of the RAIKO nanosatellite with paddles closed (left) and paddles opened (right), image credit: Tohoku University

EPS: RAIKO is using solar cells with 29.5% power generation efficiency. Two cells are pasted on each panel, and there are total 6 panels before the open of paddles. After a successful paddle opening, there will be total 10 panels. The power generation is 3 W before the opening of the paddles, and 5.9 W thereafter. The battery unit consists of 8 series NiMH cells (total 9.6 V and 750 mAh) for general use. The charge and discharge are controlled by voltage and temperature monitoring, and the threshold values can be changed by commands. 3)

ADCS (Attitude Determination and Control Subsystem): RAIKO is 3-axis stabilized using a magnetic torquer for actuation. Attitude is sensed with a magnetometer, 6 sun sensors, and a geomagnetic aspect sensor.

RF communications: Use of Ku-band and S-band transmitters, developed by the Addnics Corporation (Japan), and S-band and UHF band receivers. The command data transmission rate is 1.2 kbit/s for the UHF band (FSK modulated) or 1 kbit/s FSK modulated in S-band. The terlemetry data transmission rate is 9.6 to 100 kbit/s in S-band or 9.6 to 500 kbit/s in Ku-band with BPSK modulation. The transmission rate may be changed by ground command. An orbit determination experiment is carried out using Ku-band beacon signals. The Ku-band link is a cooperative downlink experiment of Tohoku University, Wakayama University and the University of Tokyo.

C&DHS (Command and Data Handling Subsystem): The newly developed MPU (Main Processor Unit) is shown in Figure 4. Commands which are received from the ground station are decoded by the MPU and PCU (Power Control Unit); these units feature FPGA devices. The PCU can only control the functions of power on and off of the satellite components and change the battery charging parameters. The MPU can control advanced command controlling functions. The PCU has also a reboot function. In this configuration, the PCU can shut down the MPU as well as the power of other mission components. The MPU controls the cameras, sensors and generates the telemetry data stream. The imagery taken by cameras are saved onboard in the FLASH memory of the MPU.

Spacecraft structure: The basic nanosatellite structure is shown in Figure 5 (a). The internal configuration is shown in Figures 5 (b) and (c). As shown in Figure 5 (a), RAIKO is consist of 5 subunits. The PCU (Power Control Unit) is installed in BUS-1. The electrical Analog Board (ANA) is installed in BUS-2. The MPU (Main Processor Unit) is installed in BUS-3. The other mission components are installed in BUS-4, and -5.

RAIKO features three cameras, which are a color CMOS camera for photos of the ISS when the nanosatellite is being deployed, a color CCD camera for earth observation, and a high-sensitive CCD sensor for star observation, which is planned to be used as an attitude sensor.

The deorbit experiment of RAIKO consists of a deployable membrane mechanism (50 cm x 50 cm thin aluminized polyimide film, initially in folded configuration). The mechanism will be opened by an uplink command when the satellite altitude has decreased to an altitude of 300 km.

The method of opening this thin film is using a burn cut component mechanism; a metal film resistor is integrated. At the end of the mission, the burn mechanism requires current from the spacecraft for the heat generation to cut the wire of the mechanism. In this way, the thin membrane can open on orbit.

Launch: The HTV-3 (Kounotori-3) module of JAXA, a cargo transfer vehicle to JEM-Kibo of the International Space Station, was launched on July 21, 2012 on the H-IIB launch vehicle from TNSC (Tanegashima Space Center), Japan.
Five CubeSats were part of the HTV-3 payload. The are planned to be deployed by the JSSOD (JEM-Small Satellite Orbital Deployer) later in 2012. The CubeSats are:

In addition, the J-SSOD system was delivered on this flight to the ISS and installed in JEM/Kibo. The deployment of all CubeSats was planned for Sept. 2012.

Orbit: The ISS is in a near-circular orbit in the altitude range of ~420 km, inclination = 51.6º.

Deployment of CubeSats from the ISS:

J-SSOD (JEM-Small Satellite Orbital Deployer) onboard of JEM/Kibo: The J-SSOD is a platform that acts as an interface between operations inside and outside the ISS. Two rectangular, spring loaded canisters accommodate up to 3 small 1U CubeSats each. The back plate or deck provides the needed attachment points for the JEM Slide Table for passage through the JEM airlock. Satellites (CubeSats) are installed in J-SSOD by crew members, attached to the MPEP (Multi-Purpose Experiment Platform) and passed through the JEM airlock for retrieval by the JEMRMS (JEM Remote Manipulator System). A JEMRMS grapple fixture supports the capture, orientation and deployment operations, including communications and power interfaces. 4)5)

• On October 4, 2012, the five CubeSats were successfully deployed from the new J-SSOD. The first pod contained RAIKO and We-Wish, while the second pod contained FITSat-1, F-1 and TechEdSat. 6)7)8)

The deployment from the fairly low orbit of the ISS (419 km) will limit the operational life of the CubeSats to a few months due to the encounter of atmospheric drag.

Figure 10: Photo of RAIKO and We-Wish from the ISS a few minutes after deployment (image credit: JAXA, NASA)

Mission status:

• The satellite operation was finished by orbital decay on August 6, 2013. Telemetry data were received in a total of 123 passes (in 10 months), in which 63 images were obtained. 9)

RAIKO is the mission to demonstrate the first dedicated drag sail, scaled to deorbit a nanosatellite with a 50 cm x 50 cm aluminized polyimide sail, from an orbital altitude of 300 km.

From an analysis of the housekeeping data, the following could be obtained: the solar generation power in sunshine was 3.38 W on average, the battery discharge voltage remained operational throughout the mission, the temperature of onboard computer was in the range of 20.8- 29.0 ºC, and the battery temperature was 4.2ºC on average. The real flight data from the half-year operation will be precious information for future nanosatellite projects.

- In the 20 days before the orbital decay, the command link could not be established, so the final communication was July 15, 2013. During this period, the satellite beacon signal of 13 GHz was received every day, so it is estimated that the power was not serious condition and the orbital tracking was normal.

- Until April 13, 2013, telemetry data of the RAIKO nanosatellite were successfully received in 94 passes, while imagery was obtained in 53 passes.

- On October 6, 2012, which was the second day after the satellite deployment, the command communication between RAIKO and the Tohoku University ground station, and the telemetry data from RAIKO was firstly observed.

- After deployment from the ISS on October 4, 2012, the gradual separation of RAIKO from the ISS could be confirmed using the color CMOS camera.

Two antennas for each band are installed on counter panels except for 4). In the default configuration just after the satellite separation, 1) is always powered on, and 2) is repeating in intervals of 5minutes on and 5 minutes off, for power saving. The other transmitters are powered on by ground commands.

The command data speed is 1.2 kbit/s FSK (U-band) or 1 kbit/s FSK (S-band), and the telemetry data speed is 9.6 kbit/s to 100 kbit/s in S-band, or 9.6 kbit/s to 500 kbit/s in Ku-band with BPSK modulation, the speed can be changed by a ground command.

In daily operations, three ground stations are participating:

1) U-band uplink and S-band downlink by Tohoku University with a 2.4 m diameter antenna

2) S-band uplink and Ku-band downlink by Kagoshima University with a 1.4 m diameter antenna,

3) S-band downlink by Fukui University of Technology with a 10 m diameter antenna (Figure 11).

Usually, the S-band commands are sent from the Kagoshima University, remotely operated from Tohoku University, and the S-band telemetry is received at Tohoku University and Fukui University of Technology. The Kagoshima station is located at a distance of ~1100 km southwest, and the Fukui station is located at about 400 km southwest of the Tohoku station.

At the Kagoshima station, the Ku-band beacon signals are also received by a small antenna of 45 cm in diameter. The radio frequencies are analyzed using a spectrum analyzer and a computer software analyzer, and the observations are used to study the atmosphere disturbance determination and the orbit determination.

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net)